1. Field of the Invention
This invention concerns presses and more particularly presses having a ram which is mounted for swinging movement, such as is used in cutoff apparatus for severing lengths of elongated stock emanating from a tubing mill or other such source.
2. Description of the Prior Art
In the past, presses have incorporated rams operated by power cylinders, such as large diameter air cylinders. In these arrangements typically the ram would be mounted to the output member of the power cylinder, and the air cylinder would be stroked against the bias of return springs. The application of such cylinder-operated presses to tubing or other elongated stock cutoff apparatus has been limited for several reasons to relatively light duty situations. Firstly, the ram mechanism, if mounted directly to the output piston of the power cylinder has been limited in size by the size of the power cylinders, since the ram was typically guided in its stroke by the cylinder structure, or else additional ways or slides were by necessity required. Since the cost of power cylinders increases disproportionately with increasing cylinder bore size, it has been found to be economically unfeasible to operate rams over a certain size by means of air cylinders. In addition, the typical arrangement of stroking the press against the bias of return springs has the disadvantage that the available force of which the ram would be capable of exerting would be proportionately reduced as the return springs were compressed. This disadvantage is aggravated in the usual situation in which maximum force is required at the extreme position of the ram, and necessitates substantially increased cylinder size and/or operating pressure requirements to obtain force levels adequate to operate the cutoff die set.
In other contexts, power cylinders have been coupled with force-multiplying mechanisms, such as toggle link mechanism and the ram stroked vertically upward to obviate the need for return springs or double acting cylinders. However the weight of the ram in this design would also act to reduce the available force exerted by the ram as the ram was stroked by the power cylinder. In addition, the cylinder controls tended to be rather complex and subject to the burdensome maintenance requirements, since the cylinder would be depressurized and the return springs or ram weight utilized to return the ram to its initial position.
Still another problem associated with the use of so-called double action power cylinders of the type mentioned above relates to the fact that these cylinders normally deliver less force on the return or retraction stroke thereof than on their drive or extension stroke. This difference in stroke force is a consequence of the output shaft being directly secured to one face of the cylinder's piston. Since the output shaft must be of substantial cross sectional area in order to withstand the relatively heavy loading thereof, the amount of surface area upon which fluid may exert pressure is substantially less on the piston face to which the output shaft is connected compared to the opposite face. Thus, in the past, it was necessary to select a larger power cylinder whose return stroke force satisfied a particular application.
In some applications, the timing of the press operation is critical, as in those cutoff press apparatuses involving cutting on the fly or cutting of the stock as it rapidly emanates from a stock production mill, such as a tubing or extrusion mill, in which the entire cycle must of necessity be carried out with relatively precise timing. These design problems have limited the application of such cylinder-operated presses to the aforementioned stock cutoff applications.
In such apparatus, it has been the practice to provide a swinging ram type press in which a ram member has been supported on a pair of pivotal links which constrain the ram movement to that of a swinging motion about the pivotal support of the links, its pivotal movement producing both translation in the direction of the movement of the stock, as well as a reciprocation thereof of the ram transverse to the direction of movement of the stock. A typical example of such a press is disclosed in U.S. Pat. No. 3,288,011. In this design, the ram is driven so as to be swung or oscillated about these pivotally supported links by means of a crank mechanism driven by an electric motor and clutch, the crank mechanism being connected to the connecting rod to the ram to induce the swinging movement. The weight of the ram acts in concurrence with the downward and forward movement of the ram induced during the ram stroking in a forward direction, with the geometry of the links, etc. producing the full stroking of the ram without the need for reversal of the electric motor or precise control over the crank mechanism or electric motor and clutch.
The swinging movement of the ram in turn produces operation of the cutoff die set which is adapted to be reciprocated by the ram as it travels with the stock on an upper rail set carried by the ram and a lower rail set fixed to the machine base. The cutoff die set, as described in the aforementioned U.S. patent, includes means for initially clamping the die set to the stock to be severed, causing the die set to traverse the rail set together with the stock. Subsequently, downward movement of a cutoff blade, included in the die set is induced by the downward movement of the ram moving through its arcuate path as it swings about the pivotal supports provided by the pivotal links. Continued rotation of the eccentric crank drives the ram to its full down position with further rotation producing a reversal of movement of the swinging ram, to first withdraw the cutoff blade, then releasing the stock from the die set to allow it to be returned to its initial position by means of a return cylinder or other mechanism prior to initiation of a new cycle. A variation of that basic mechanism is disclosed in co-pending patent application, Ser. No. 715,559, filed Aug. 18, 1976, now U.S. Pat. No. 4,228,706. In that application an adjustable length connecting rod is provided which serves to provide a capability for shifting the segment of the arcuate path through which the ram is constrained to move by virtue of its support on the pivotally supported links, which shifting provides for adjusting the shut height or the position of the ram in its full down position, as well as the length of its stroke in such a way as to adapt the cutoff apparatus to die sets of varying configurations, to accommodate its application to varying tube size etc. in a manner described in that application.
While these machines have performed very satisfactorily and are adapted to reliably stroke the ram through its required swinging movement, the electric motor, clutch, and eccentric crank components comprise a considerable element of manufacturing cost in the apparatus.
On the other hand, while the aforementioned cylinder-operated presses suffer from the disadvantages described, they do exhibit the inherent advantage of a generally lower manufacturing costs, due to the use of simple power cylinders as a source of operating means for the ram where cylinders of a reasonable size are able to be utilized.
Accordingly, it is an object of the present invention to adapt a power cylinder to a swinging ram cutoff press of the sort described.
It is a further object of the present invention to adapt such power cylinder to the cutoff mechanism described in such a way as to not necessitate the use of complex controls or adversely affecting the reliability of the machine.
It is yet another object of the present invention to provide such an adaptation which does not involve the use of return springs tending to reduce the available force generated by the cylinder during stroking of the ram.
It is a further object of the present invention to incorporate a power cylinder operating device into a swinging ram type cutoff apparatus in such a way as to enhance the available force at that portion of the ram's stroke requiring maximum force to be exerted by the ram.
It is yet another object of the present invention to provide such an adaptation without entailing the incorporation of expensive and precision structural control components.
A still further object of the present invention is to provide a swinging ram apparatus driven by a power cylinder of the type delivering less force on its return stroke than on its extension stroke, in which means are provided for increasing the force transmitted to the ram on the cylinder's return stroke in order that a cylinder of minimal size may be effectively employed in each particular application.